Stabilized alpha-cyanoacrylate adhesive compositions

ABSTRACT

AN ADHESIVE COMPOSITION CONTAINING AN AROMATIC SULFONIC ACID AS A STABILIZER. THIS COMPOSITION CAN BE INCREASED IN TACKINESS, WITHOUT CAUSING LENGTH, BY ADDITION OF AN ACRYLATE ESTER-ACRYLONITRILE COPOLYMER.

United States Patent US. Cl. 260-464' 7 Claims ABSTRACT OF THE DISCLOSURE An adhesive composition containing an aromatic sulfonic acid as a stabilizer. This composition can be increased in tackiness, without causing length, by addition of an acrylate ester-acrylonitrile copolymer.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to stable adhesive compositions. More particularly, the invention pertains to stable acyanoacrylate adhesive compositions which, at the time of application as adhesives, are polymerizable within quite a short period of time but, at the time of storage, are inhibited from polymerization.

(2) Description of the prior art It is well known that an a-cyanoacrylate represented by the general formula wherein -R is a C -C alkyl group, a cyclohexyl group or a phenyl group, has such a property that when formed into a thin film, it is anionically polymerized, without any particular addition of catalyst, in such a short period of time as several seconds to several minutes due to a slight amount of moisture present in the air, and that when used as an adhesive, it can provide an adhering power extremely high in strength. By virtue of the abovementioned characteristic, the a-cyanoacrylates are used, as one-liquid type instantaneous adhesives, for the bonding of substantially all of organic and inorganic substances, such as rubbers, plastics, metals, fibers, leathers, etc.; for the bonding of parts of electric appliances, precision instruments and household articles; and further for the bonding of blood vessels in surgical operations. In addition thereto, they have been utilized not as mere adhesives but as fillers for filling small cavities or cracks in the therapy of decayed teeth.

Thus, the u-cyanoacrylates have been advantageously used in various fields. They have, however, such a great drawback that even when stored in tightly closed vessels in a state shielded from moisture in the air, they polymerize within a relatively short period of time, if they are allowed to stand at normal temperature, and said period of time becomes shorter with increasing storage temperature.

In storing the u-cyanoacrylates, therefore, they are made high in stability by using an anionic polymerization inhibitor in the form of an acid gas, such as sulfite gas, nitrogen dioxide or hydrogen fluoride, in combination with a free radical polymerization inhibitor such as hydroquinone, tert-butyl catechol or monomethyl ether of hydroquinone (refer to US. Pats. 2,794,788 and 2,765,332).

3,652,635 Patented Mar. 28, 1972 "ice As mentioned above, however, the anionic polymerization inhibitor, which is a main component of the conventional stabilizer, is gaseous at normal temperature. Accordingly, in adding a definite amount of the inhibitor to the a-cyanoacrylate, a part thereof escapes without being dissolved, and therefore the inhibitor is difiicultly added in an accurate amount. Moreover, when an inhibitor-incorporated a-cyanoacrylate is stored for a long period of time or is stored while using the same intermittently, there are even such cases where the inhibitor spontaneously escapes from the monomer. Thus, it is difiicult to impart complete stability to a-cyanoacrylates.

DISCLOSURE OF THE INVENTION The present invention has been established in order to cope with such circumstances as mentioned above.

The first object of the present invention is to provide an a-cyanoacrylate composition containing a stabilizer,

which can be accurately added to the a-cyanoacrylate, scarcely escapes during storage, and can thoroughly stabilize the ot-cyanoacrylate.

The second object of the invention is to provide an ix-cyanoacrylate composition increased in tackiness which is stable and is less in length.

The first object of the invention can be accomplished by adding a solid aromatic sulfonic acid to an a-cyanoacrylate.

Aromatic sulfonic acids are less volatile than the conventionally employed S0 stabilizers, so that they do not vary in stabilizing effect over a long period of time. Further, they are highly quantitative at the time of addition, and hence can maintain the uniformity in quality of the resulting mixtures. Accordingly, an a-cyanoacrylate incorporated with a suitable amount of the aromatic sulfonic acid shows favorable storage stability even at an elevated temperature and does not polymerize over an extremely long period of time at room temperature, which is an ordinary storage temperature. When brought into the form of a thin film, however, said a-cyanoacrylate instantaneously polymerizes without application of heat or pressure or without addition of any polymerization catalyst, as in the case of an ot-cyanoacrylate incorporated with no aromatic sulfonic acid, and the bonding strength attained is sufliciently high when viewed from the practical standpoint.

Examples of the aromatic sulfonic acid employed in the present invention include benzenesulfonic acid [C H SO H], p-toluenesulfonic acid [=CH -C H SO H], p-xylene-Z-sulfonic acid [(CH C H SO H], p-phenolsulfonic acid [C H (OH)-SO H], l-naphthalenesulfonic acid [C H SO H] and p nitrobenzenesulfonic acid [C H (NO -SO H]. The amounts of these aromatic sulfonic acids to be added to a-cyanoacrylates are within the range of 0.0001 to 0.01% by weight. Practically, however, the amounts within the range of 0.001 to 0.003% by weight are preferable. If the amounts thereof are less than said range, no sufficient storage stability is displayed, while if the amounts are more than said range, a relatively long period of time is required at the time of initial bonding, or the lowering of bonding strength is brought about. An a-cyanoacrylate incorporated with the aromatic sulfonic acid has sufficient storage stability for practical purposes, even when it is used independently, but may further be incorporated with 0.005 to 0.5% by weight (based on the monomer) of a known radical polymerization inhibitor such as hydroquinone or monomethyl ether of hydroquinone.

Examples of a-cyanoacrylates capable of being stabilized in accordance with the present invention include a-cyanornethyl acrylate, ot-cyanoethyl acrylate, u-cyanon-propyl acrylate, a-cyanoisopropyl acrylate, a-cyanobutyl 3 acrylate, a-cyanoisobutyl acrylate, a-cyanoamyl acrylate, u-cyanocyclohexyl acrylate, a-cyanolauryl acrylate, occyanocapryl acrylate and a-cyano-2-ethylhexyl acrylate.

Now, the second object of the present invention is ex- 4 down time (sec.) at 30 C., and the average values of the solution and the acetone are represented by t and t respectively. Using these values, the viscosity of the copolymer is calculated according to the following equaplained below. 5 tion. ot-Cyanoacrylate is a substance which is extremely high t in permeability. Accordingly, in applying the oc-cyanov 1 acrylate to a porous material, e.g. paper, leather, wood or cloth, it has heretofore been incorporated with such a viscosity-increasing agent as, for example, an a-cyanoalkyl 10 z aggg Fgl g acrylate polymer, an acrylate ester polymer, a cellulose ester or the like. The present inventors have found, how- The present invention is illustrated below with referever, that acrylate ester-acrylonitrile copolymers are partence to examples and comparative examples. ticularly excellent as compared with the convent1onal v1s- Examples F50 and Comparative Examples cosity-lncreasing agents. That 1s, the above-mennoned t copolymers have such advantages that when added to a- To an -Y l acrylate? mollomer Were lndlvldually n l te h id fa o bl ili and i added such aromatic sulfomc acids as benzenesulfomc cosity, are less in length, and give plasticity to a-cyanoa p-toluenesulfqmc n n-p q and and 1 3- acrylate polymers after curing to make them less brittle nltrollenzfilleslllfiomc acld, elthef Independently 111 than conventional polymers of this kind. Among the said comblnatlon Wlth fnonomethyl ether of hydroqulnone copolymers, those containing an acrylate ester whose (hereinafter abbfevlated as Q) l P p alkyl group has 4 or more carb n at are 1 i ples. For comparlson, control samples which had not been solubility for a-cyanoacrylates. It is therefore preferable Incorporated with aromatlc Sulfonlc aclds f P to use copolymers containing an acrylate ester whose alkyl These pl and C0I1tff 1 Samples were mYestlgated In group has 1 to 4 carbon atoms. Examples of such acrylate 5 storage stability and bonding strength to obtam the results ester include methyl acrylate, ethyl acrylate, propyl acry- Set forth in es la late, isopropyl acrylate, butyl acrylate and isobutyl acry- The Storage stablllty was tested y Charging of late. each sample in a 20 ml. polyethylene-made vessel, tightly The composition ratio of the acrylate ester-acrylonitrile closing the vessel as it was without substituting the air copolymer is preferably such that the proportion of the p esent in the upper space of the vessel by an inert gas acrylate ester in the copolymer is 60-90% by weight or the like, and then allowing the vessel to stand at room based on 100% by weight of the copolymer. Although the temperature or in a thermostat. The test in thermostat was adoption of an acrylate ester proportion out of said range effected at 60 C. in order to confirm that the samples of is not objectionable, difiiculties in solubility and hardness the present invention are stable even at elevated temperaare brought about with increasing proportion of the tures. acrylonitrile component. The bonding strength was measured in such a manner The solution viscosity of the copolymer is preferably that a definite amount (0.005 g.) of each sample imabout 2 to 4 when represented by asp/c (where c is the mediately before storage or during storage was applied amount (g.) of the copolymer in 100 cc. of an acetone onto the cross-section of a rigid polyvinyl chloride test solution thereof). 1 is measured in the following manner: piece of 5 mm. in thickness, 20 mm. in width and '35 mm. 0.2 g. of the copolymer is accurately weighed into a in length (application area 10 cm. and the test piece 100 cc. messflask and is dissolved in acetone to make 100 was bonded at said cross-section, with rubbing, to another cc. This solution and acetone itself are subjected intest piece of the same quality and, after a definite period dividually to a Ubbelohdes viscometer (or an Ostwalds of time (24 hours), was measured in tensile strength by viscometer) and are measured 3 times or more in flowuse of an Amsler-type tensile testing machine.

TABLE 1 Stabilizer Amount of Amount MEHQ added (wt. added (wt. Tempera- Kind percent) percent) ture 0.) Stable period Comparative Example:

1 N0 addition...:.;:;:::;. 0 0 5 days. 2 -do 0 0 1 day. 3..-- .do.... 0 0. 005 60 1 day.

Example:

1 Benzenesulfonie acid. I 0. 001 0. 005 More than 3 months (lo 0.001 0. 005 60 More than 30 days.

0. 001 0. 005 60 Do. 0.002 0 More than 6 months.- 0. 002 0 60 More than 30 days. 0.002 0 00 Do. 0. 003 0. 005 More than 6 months: 0. 003 0. 005 60 More than 30 days. 0. 003 0. 005 60 Do. 0. 004 0 More than 6 months 0. 004 0 60 More than 30 days. 0. 004 0 60 Do. 0. 005 0 (I) More than 6 months 0. 005 0 60 More than 30 days. 0. 005 0 60 Do.

16 p-Toluenesulionic acid 0. 001 0.01 More than 3 months 17.. dn 0. 001 0. 01 60 More than 30 days. 18 do 0.001 0. 01 60 Do.

do 0. 002 0 More than 6 months;

0.002 0 60 More than 30 days. 0.002 0 00 Do. 0.003 0 More than 6 muntn 0.003 0 60 More than 30 days. 0. 003 0 60 Do.

25 p-Phenolsulfonlc acid 0. 001 0 More than 3 months 26.-. do 0.001 0 60 More than 30 days.

0.001 0 60 Do. 0. 002 U. 01 0) More than 6 months.

'IABLE 1.'Constlnued Stabilizer Amount Amount MEHQ added (wt. added (wt. Tempera- Kind percent) percent) ture 0.) Stable period Exam le:

29? p-Phenolsulphonic acid 0. 002 0. 01 60 More than 30 days.

do 0. 002 0. 01 60 Do.

0. 003 0 More than 6 months. 0. 003 0 60 More than 30 days. 0.003 0 60 Do.

0.001 0.005 More than 6 months. 0.001 0.005 60 More than 80 days. 0. 001 0. 005 60 Do. 0. 002 0 More than 6 months. 0. 002 0 60 More than 30 days. 0. 002 0 60 Do. 0.003 0 More than 6 months. 0.003 0 60 More than 30 days. 0.003 0 60 Do.

1 Room temperature.

TABLE 2 Stabilizer Amount Amount of MEHQ Tensile strength (kg/cm?) added added Temper- (w (wt. ature 10 2 3 6 Kind percent) percent) 0.) days days days days months months months 0 0 6g g E l N addition 0 0 4 5 Camparatrve xamp e o 0 0 20 356 Example: 0 002 0 ulf (8 acid. 0. 002 0 43.. Benzenes 0m 0. 002 0 20 352 0. 003 0.005 60 347 44 .do 0. 003 0. 005 347 0. 003 0. 005 20 347 0. 002 g Z58 -'I 1 all i acid 0.002 5 45. p 0 uenes on c 0. 0 2 0 20 350 0.003 g 225 do 0.003 5 46 0.003 0 20 345 -88 8-8 88 282 h lsulf acid-. 0. 2 1 p P em 0m 0 002 0.01 20 355 8' 882 8 28 233 48 01004 0 20 sis 888 8 28 -N't l0 ulfonic acid-.. 1 49.- p 1 r0 enzenes 0.0 1 0 20 356 -888 8 88 881 0. 50 0. 003 0 20 344 1 Polymerized.

The term polymerized appearing in the column tensile strengt in Table 2 indicates that when the sample was taken out on the 10th day from the initiation of storage at, for example, C., as in the case of Comparative Example 4, the sample had already polymerized and was not usable.

As is clear from Tables 1 and 2, a-cyanoacrylates stabilized in accordance with the present invention are markedly excellent in storage stability.

Examples 51-68 and Comparative Examples 5- 38 ot-Cyanoacrylate compositions comprising each monomer, a viscosity-increasing agent and 0.006% by weight of p-toluenesulfonic acid as a stabilizer were investigated in solubility, viscosity, length, coloration and bonding strength to obtain the results set forth in Tables 3 and 4, Further, the said compositions were investigated in relationship between the solubilities of the compositions and the proportions and compositions of the acrylate esteracrylonitrile copolymers employed, to obtain the results shown in Table 5.

The solubility of each composition was measured in such a manner that the viscosity-increasing agent, which had been finely divided into a definite size, was added to each a-cyanoacrylate monomer, and the dissolved state of the mixture, after shaking at room temperature for 24 hours, was evaluated by visual observation. The viscosity was decided in such a manner that the tackiness of each composition after dissolution of the viscosity-increasing agent was visually evaluated or was measured by means of a Brookfield viscometer. The length was evaluated by dipping the tip of a glass rod in the composition after dissolution of the viscosity-increasing agent and taking up the glass rod to visually observe the state of the composition on the tip of the glass rod. The coloraion was evaluated by the visual observation of the color tone of the composition after dissolution of the viscosity-increasing agent. The stability was tested in such a manner that 15 g. of each composition was charged into a 20 ml. polyethylene-made vessel, and the vessel was tightly closed and then allowed to stand at room temperature or in a thermostat at 60 C. and at a relative humidity (RH) of 55%. The tensile strength was measured in such a manner that a drop of the composition was applied to the cross-section of a rigid polyvinyl chloride test piece of 20 mm. in width, 35 mm. in length and 5 mm. in thickness, was closely adhered, with rubbing, to another test piece of the same quality, was allowed to stand at room temperature for 24 hours and was then subjected to an Amsler-type tensile testing machine. The impact strength was measured by impacting with a U-F type impact testing machine the bonded portion of two rigid polyvinyl chloride test pieces which had been bonded to each other in the same manner as mentioned above. Further, the solution viscosity of the acrylate ester-acrylonitrile copolymer employed in each example was3 .0-3.5.

TABLE 3 Viscosity-increasing agent (Polymer) Amount Stable period added (wt. Solu- Vis- Colora- Room 60 C./55% Monomer Kind percent) bility ccsity Length tion temperature RH Example No.:

51 Ethyl a-cyano- Methyl acrylate/acrylo- 2 O O O O More than 6 More than 1 acrylate. nitrile, 80/20. months. month. 52 ..do Ethyliacrylate/acrylonitrile, 2 O O O O '....do Do. 5a.. .-.-do-..---.------ B 1% cr latelacr lonitme, 2 O O O .....do Do.

Cgqmparative Example 0.: Ethyl a-cyano- Nitrlle rubber 2 O A O A 1 month"... 8 days.

acrylate. 6 --do Cellulose acetate 2 A Cellulose propionate 2 O A O O 3 months.- 21 days. Methyl acrylate 2 O O X O More than 6 More than 1 months. month. Ethyl acrylate 2 O O X O .do D0. Butyl acrylate 2 O O X O .d0 Do. 2-ethylhexyl acrylate 2 X Methyl methacrylate (high 2 O O X O Do.

polymerization degree). Methyl methacrylate (low 2 O A O O Do.

polymerization degree). Ethyl a-cyanoacrylate-. 2 O O X O D0. 3 2 O X O Do. 2 O A O O More than 6 Do.

months. 18 do Methyl methacrylate/buta- 2 A dlene/styrol. 19 ..do Acrylonitrile/butadiene/ 2 O A A A styrol.

N 0TE.Mal'k O represents favorable; Mark A represents somewhat favorable; Mark X represents poor.

TABLE 4 Viscosity-increasing agent (polymer) Bonding strength Amount added Viscos- (wt. ity Tensile Impact Monomer Kind percent) (cp.) (kgJcmfl) (kg. cmJcmfi) Ethyl a-cyanoacrylate.- Methyl acrylate/acrylonitrile, 80/20- 2.1 92 351 16.2 .do--- Ethyl acrylate/acrylouitrile, /25 2. 0 102 348 16. 5 56 -.do Butyl acrylateacr/ylonitrile, 70/30 1. 8 97 355 17. 3

57 Butyl wcmanoacrylate- Methyl acrylate/acrylonltrile, /20- 2. 1 91 219 10. 8 58 do Ethyl acrylate/acrylonitrlle, 75/25 2. 0 98 218 11. 1 59 do. Butyl acrylate/acrylonitrlle, 70/30 1. 8 96 223 12. 1

Comparative Example No.:

20 Ethyl a-cyanoacrylate.... Cellulose propionate.-.-... 4. 6 108 319 13. 7 21 (in Ethyl acrylate. 4. 8 104 324 14. 1 29 do- Butyl acrylate 4. 5 94 318 13. 6 23 fl 0 Methyl methecrylate 5. 1 305 13. 2 24 d Butyl a-cyanoacrylate 4. 8 112 323 14. 0

25 Butyl a-cyanoacrylate Cellulose propionate 4. 6 106 188 8. 9 26 do Ethyl acry1ate.-.. 4. 8 103 176 9.2 27 do- Butyl acrylate. 4. 5 96 8. 6 28 do- Methyl methacrylate. 5. 1 104 182 8. 8 29 do Butyl a-cyanoacrylate 4.8 101 178 8.7

TABLE 5 Stabilizer Viscosity-increasing agent (polymer) Amount Amount added (wt. added (wt. Solubility Monomer Kllld percent) Kind Ratio percent) Example N 0.:

60 Y Ethyl a-eyanop-Toluenesul- 60 Methyl acrylatel 60-90/40-10 2. 1 Favorable.

acrylate. fonlc acid. acrylonitirile. 61 do do 60 Ethyl acrylate/ 60-90/40-10 2.0 Do;

acrylonitrile. g (10 I dn 60 Butyl acrylatel 60-90/40-10 1. 8 Do.

acrylonitrile.

63 Propyl a-cyano- Benzenesul- 60 Methyl acrylatel 60-90/40-10 2. 0 Do.

acrylate. Ionic acid. acrylonitrlle. 64.. fin 60 Ethyl acrylatel 60-90/40-10 2. 0 Do.

acrylonitrlle. 65.. dn 60 Butyl acrylutel 60-90l40-10 2. 0 Do.

acrylonltrile.

66m. Butyl a-cyanoo-Ni robenzene- 60 Methyl acrylate/ 00-90l40-10 2. 0 Do.

acrylatle. sulfonic acid. aorylonitrile. 67 e (in n r 60 Ethyl acrylate/ 60-90/40-l0 2. 0 Do.

acrylonitrlle. 68...... .d0..... do-....';.-.:-:: 60 Butyl acrylate/ 60-90/40-10 2. 0 Do.

acrylonitrlle.

TABLE 5.-Cntinued Stabilizer Viscosity-increasing agent (polymer) Amount Amount added (Wt. added (wt. Solubil- Monomer Kind percent) Kind Ratio percent) ity Example No.

30 Ethyl a-cyanop-Toluene-sul- 60 Methyl aorylate/ l0-50/90-50 2.0 Somewhat acrylate. tonic aeidl acrylonitrile. p r. 31 d0 dn 60 Ethyl acrylate/ -50/90-50 2.0 Do.

acrylonitrile. 32 dn dn 60 Butyl aoi'ylate/ 10-50/90-50 2.0 Do.

acrylonitrile.

Comparative Example No.:

33 Butyl a-eyano- Benzenesulfonie 60 Methyl acrylate/ 10-50l90-50 2.0 Somewhat acrylate. acid. acrylonitrile. poor. 34 do do 60 Ethyl aerylate/ 10-50/90-50 2.0 Do.

acrylonitrile. 35 do do 60 Butyl acrylate/ 10-50/90-50 2.0 Do.

aerylonitrile.

36 Methyl a-eyanop-Toluene sul- 60 2.0 Somewhat acrylate. ionic acid. 60 poor. 37 Ethyl 60 2-ethylhexyl acrylate/ 10-90/90-10 acrylate' aerylonitrilo 38 Butyla-cyanodo 00 2.0 Do.

acrylate.

While the above has been described in connection with preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is aimed, therefore, to cover in the appended claims all such changes and modifications as falling within the true spirit and scope of this invention.

What is claimed is:

1. A stable adhesive composition consisting essentially of monomeric ester of a-cyanoacrylic acid having the formula wherein R is a member selected from the group consisting of an alkyl group having 1 to 16 carbon atoms, a cyclohexyl group and a phenyl group, and as a stabilizer from about 0.0001% to about 0.01% by weight of an aromatic sulfonic acid based on the weight of said monomeric ester, said aromatic sulfonic acid being selected from the group consisting of benzene sulfonic acid, p-toluene sul; fonic acid, p-phenyl sulfonic acid and p-nitrobenzene sulfonic acid.

2. A composition according to claim 1, wherein said composition contains 0.001 to 0.003% by weight of said aromatic sulfonic acid stabilizer.

References Cited UNITED STATES PATENTS 2,721,858 10/1955 Joyner et a1 260465.4 X 3,355,482 11/1967 Coover, Jr. et al. 260-4654 X JOSEPH P. BRUST, Primary Examiner US. Cl. X.R. 

